This invention relates generally to microwave circuits and, more particularly, to microwave power dividers.
As is known in the art, a common circuit employed in many microwave system applications is a so-called in-phase power combiner. Simply speaking, an in-phase power divider is a circuit which takes an input radio frequency signal and provides two or more output signals in-phase and of equal or unequal power in accordance with a particular application. There are many known power divider/combiner circuits, in particular one such circuit is described in an article entitled "An N-way Power Divider" by E. Wilkinson, IEEE Transactions on Microwave Theory and Techniques, MTT-8, No. 1, January 1960, pages 116-118. Described in this article is the so-called Wilkinson power combiner/divider which has applications in many microwave systems. Generally, most power combiner/dividers are even multiple output port types. In order to provide an odd output port type, generally an odd number of transmission line paths are provided to be coupled to a common transmission line path and each of the transmission line paths are balanced with resistors placed between the lines and a floating node. This approach is a three dimensional approach since the use of a floating node requires a non-planar interconnection of the resistors. This approach is not particularly suitable for using microwave strip type integrated circuit fabrication techniques.
An alternative approach to the floating node approach mentioned above, is a planarized approach in which the balanced resistors rather than being placed at floating nodes are disposed in shunt across the arms of each of the output transmission line paths. This so-called planarized power divider, although adaptable for use to provide an odd number of output stages which is fabricated in a common plane, nevertheless, has several drawbacks. For instance, in a microstrip implementation of the planarized power divider, relatively high impedance transmission lines are required and at microwave frequencies these high impedance transmission lines are very narrow strip conductors which are difficult to fabricate. More importantly however, such narrow lines increase the insertion loss of the power divider circuit.
Future applications of these circuits require an approach in which it is relatively easy to provide an unequal power division between one of the branches and which can be easily integrated with monolithic microwave integrated circuit technology. Therefore, the non-planar approach described above is particularly unsuited. Moreover, the circuit should have very good microwave characteristics and thus the high insertion loss and low isolation, as provided by the planarized approach also mentioned above, will be unsuited.
Applications for this type of circuit would include, for example, a wide-band receiver having both amplitude and phase tracking requirements. Such a 3-port in-phase power divider can be used in a local oscillator distribution chain in such a receiver where one channel is used as a calibration channel and is fed at a lower level of local oscillator power thereby permitting more local oscillator power to be provided to the two receiving channels. This would improve the dynamic range of the receiver by maximizing local oscillator power to the signal channels that are being processed in the receiver while still permitting the use of a separate calibration channel.